A growing area in the field of printing is known as flexography or flexographic ink printing. Flexographic ink printing is a branch of rotary typographic printing in which the printing is applied to a print-receiving substrate by use of a flexible relief plate with highly fluid, volatile inks which dry rapidly by evaporation. Flexography is widely utilized for printing on plastic films.
Another process which is widely utilized for printing on plastic films is the gravure process. In this process the printing image is engraved into a cylinder in the form of cells which become filled with ink. Printing is achieved by passing the substrate between the gravure cylinder and an impression roller under pressure.
A flexographic or gravure printing ink generally contains three basic types of ingredients denominated as a solvent, a colorant, and a binder. Minor amounts of other additives also may be employed to provide the desired characteristics (i.e., rheology, viscosity, etc.) for the printing ink composition.
In recent years, increased emphasis has been placed on the use of water as the solvent, rather than an organic solvent. In keeping with this trend, a wide variety of colorants or pigments have been developed for use in water-based ink formulations.
The binder component of the printing ink composition generally comprises a resin which functions primarily to increase adhesion of the pigment to the substrate, while also often acting as a dispersing medium and carrier. Specific acrylic polymer latexes are commonly employed as binders in water-based printing ink compositions.
However, one of the major shortcomings of using water-based inks (relative to the traditional solvent-based alternatives) for printing on plastic film is a lack of chemical resistance. That is, certain chemicals tend to cause water-based inks to loose their adherence to plastic films, thereby making the ink smear or run. Thus, good chemical resistance is a highly desired characteristic because of the environments to which many printed packages are exposed.
Therefore, it is the object of this invention to produce acrylic latex binders for use in preparing zinc-containing water-based printing inks which, when utilized for printing on plastic films, exhibit increased chemical resistance.
A further object of this invention is to produce chemical resistant aqueous printing inks.